It is well known for lubricating oils to contain a number of additives used to protect the mechanical devices such as internal combustion engines from wear, soot deposits and acidity build up. A common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP). It is believed that ZDDP antiwear additives protect the engine by forming a protective film on metal surfaces.
In recent years engine lubricants containing phosphorus compounds and sulphur have been shown to contribute in part to particulate emissions, and emissions of other pollutants. In addition, sulphur and phosphorus tend to poison the catalysts used in catalytic converters, resulting in a reduction in performance of said catalysts.
Other developments in engine oil lubricating oils have also reduced the amount of sulphur, phosphorus and sulphated ash. Thus this has typically lowered the amount of ZDDP used in the lubricating oils. However, even the reduced levels of phosphorus and sulphur from ZDDP may adversely poison the catalysts.
Consequently, it would be desirable to provide an alternative antiwear agent capable of at least one of (i) reducing or preventing phosphorus emissions, (ii) reducing or preventing sulphur emissions, and (iii) wholly or partially replacing ZDDP in lubricating oils. The present invention provides an antiwear agent capable of achieving at least one of (i) to (iii). In addition it may also be desirable for the antiwear agent to not have a detrimental affect on other components of a mechanical device e.g., a seal or provide lead and/or copper corrosion inhibition.
U.S. Pat. No. 2,604,451 discloses an adduct of an alpha hexyldecyl malonic acid (or alphacyclohexyl malonic acid) with dodecylamine. The resultant product is suitable for lubricant anticorrosion additives in e.g., internal combustion engines.
U.S. Pat. No. 4,062,788 discloses chlorophenyl malonic acid esters as suitable antiwear agents for engine oils. The chlorophenyl malonic acid esters may be used as alternatives to traditional ZDDP chemistry. The reference further discloses in an example a formulation using Qatar Marine base oil HVI60.
The use of malonic acid esters as a significant portion (20-30 wt %) of lubricating base oil is disclosed in SU 825594 and SU 810778. Specifically, SU discloses lubricating compositions with load-carrying, antiwear and antifriction performance containing malonic acid esters with C4-8 aliphatic groups. Whereas, SU 825594 discloses lubricating composition with antiwear performance containing di-C4-9-alkyl malonate.
Oxalates suitable for internal combustion engines are disclosed in U.S. Pat. No. 2,383,146 and U.S. Pat. No. 2,447,619. Specifically U.S. Pat. No. 2,383,146 discloses a lubricant containing dialkyl oxalates. Whereas U.S. Pat. No. 2,447,619 discloses sulphurised oleyl oxalates in crankcase lubricants.